Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
The use of bitumen in the manufacture of materials for highway and industrial applications has been known for a long time. Bitumen is the main hydrocarbon binder used in the field of road construction or civil engineering. To be able to be used as a binder in these different applications, the bitumen must have certain mechanical properties, and in particular elastic or cohesive properties. The mechanical properties of the bituminous compositions are determined by standardized tests of the different mechanical characteristics such as the softening point, the penetrability and the rheological characteristics in defined traction. Asphalts are performance graded (PG) by a set of specifications developed by the US federal government (Strategic Highway Research Program or SHRP). For example, PG58-34 asphalt provides good rut resistance at 58° C. (determined by AASHTO (American Association of State Highway Transportation Officials)) and good cold cracking resistance at −34° C.
In general, the conventional bitumens do not simultaneously have all of the required qualities and it has been known for a long time that the addition of acid and/or various polymers to these conventional bitumens makes it possible to modify the mechanical properties of the latter and to form modified bitumen compositions having improved mechanical qualities compared with those of the bitumens alone.
Asphalt sold for paving may be modified with polymers to improve rut resistance, fatigue resistance, cracking resistance, and can improve stripping resistance (from aggregate) resulting from increases in asphalt elasticity and stiffness. Addition of polymer to asphalt increases the higher number (provides higher temperature rut resistance) and improves fatigue resistance. Good low temperature properties are to a large extent dependent on the specific asphalt composition (e.g., flux oil content, penetration index), but the polymer type does influence low temperature performance.
The asphalt industry considers polymers for asphalt modification to be either elastomers or plastomers. Generally elastomeric polymers improve low temperature performance and plastomeric polymers decrease it. The word plastomer indicates a lack of elastomeric properties. Plastomers are sometimes used to modify asphalt because they can increase stiffness and viscosity, which improves rut resistance, but they are generally considered inferior to elastomers due to lack of significant improvements in fatigue resistance, creep resistance, cold crack resistance, etc. Styrene/butadiene/styrene block copolymers (SBS) is considered an elastomer, as are ethylene/butyl acrylate/glycidyl methacrylate terpolymer resin (EnBAGMA) and ethylene/vinyl ester/glycidyl methacrylate terpolymer resin (EEGMA), both of which are available from E. I. du Pont de Nemours and Company, Wilmington, Del., USA (hereinafter “DuPont”) under the trademark Elvaloy® RET. Polyethylene (PE) and ethylene vinyl acetate (EVA) resins are considered plastomers. PE is not miscible with asphalt, so asphalt modified with it must be continuously stirred to prevent separation. Asphalt modified with PE must be prepared at the mix plant and cannot be shipped due to separation. PE therefore acts as filler and does not meaningfully increase the softening point of asphalt.
Among the polymers added to bitumens, random or block copolymers of an aromatic monovinyl hydrocarbon and a conjugated diene and in particular of styrene and butadiene or of styrene and isoprene are particularly effective as they dissolve very easily in the bitumens and confer upon them excellent mechanical and dynamic properties and in particular very good viscoelastic properties. U.S. Pat. No. 6,087,420 describes a method for producing bitumen/polymer compositions comprising at least one styrene-butadiene copolymer.
The use of other polymers as additives to asphalt (bitumen) is well known in the art. See for example U.S. Pat. Nos. 4,650,820 and 4,451,598, wherein terpolymers derived from ethylene, an alkyl acrylate and maleic anhydride are mixed with bitumen.
Also see for example U.S. Pat. Nos. 5,306,750, 6,011,095, 6,117,926 and 6,743,838 and U.S. Patent Application Publication 2007/0027261, wherein reactant epoxy-functionalized, particularly glycidyl-containing, ethylene copolymers are mixed and reacted with bitumen and, as taught in U.S. Pat. Nos. 6,011,095 and 6,117,926, with an acid catalyst or co-reactant to accelerate the rate of reaction and lower cost of the modified system. DuPont Elvaloy® RET resins (ENBAGMA and EEGMA) are excellent modifiers for asphalt and improve asphalt performance at low concentrations (1 to 2 weight %).
The improvement in asphalt properties with addition of Elvaloy® RET at such low concentrations may be due to a chemical reaction between the Elvaloy® RET and the functionalized polar fraction of asphalt (asphaltenes).
U.S. Pat. No. 5,331,028 describes blends of asphalt with a combination of glycidyl-containing ethylene copolymer and a styrene-conjugated diene block copolymer.
U.S. Pat. No. 9,028,602 discloses a bituminous composition comprising a bitumen in an amount ranging from 20 to 90 weight %, a carboxylic additive in an amount of from 0.25 to 5 weight %, and sulfur in an amount of 5 to 75 weight %, all percentages based on the weight of bitumen, carboxylic additive and sulfur, wherein the carboxylic additive is selected from carboxylic acids, carboxylic esters and carboxylic anhydrides.
U.S. Pat. No. 7,608,142 discloses a slow setting bitumen-aggregate mix for cold paving comprising a cationic oil-in-water emulsion in the presence of an emulsifier containing a tertiary amine and an acid.
Mixing asphalt with elastomers such as EnBAGMA and EEGMA requires significant mixing at elevated temperatures to achieve the benefits of their addition. EnBAGMA and EEGMA are presented in pellet form and are added to hot asphalt where the pellets soften and melt due to the heat and the stirring. The reaction occurs with heat alone but acids such as polyphosphoric acid (PPA) are sometimes added to reduce the reaction time with asphalt. Depending on mixing conditions, it may take 6 to 24 hours without acid compared to 1 to 6 hours with acid to obtain thorough mixing. The resultant polymer modified asphalt (PMA) may not be as elastic (as evidenced by a higher phase angle and low elastic recovery) without acid. Some asphalt producers use acid and others prefer heat alone because addition of acid can be a negative in some cases. For example, acids cannot be used with amine antistrips. Furthermore, the addition of PPA to a glycidyl-containing ethylene copolymer based PMA produced from a low asphaltene asphalt results in gelling. Moreover, the amount of glycidyl-containing ethylene copolymer is limited because higher amounts result in gelling. The addition of additional glycidyl-containing ethylene copolymer to a PMA to adjust properties also results in gelling. Finally, the properties of some PMA's produced with glycidyl-containing ethylene copolymer and PPA drift down with aging at elevated temperatures.
It is also known that the stability of the bitumen/polymer compositions can be improved by chemically coupling the polymer with the bitumen. This improvement extends the field of use of the bitumen-polymer compositions. The cross-linking of the bitumen/polymer compositions confers upon them very good properties in terms of storage stability, cohesion, elongation capacity and resistance to aging.
Because of the objections to the use of polyphosphoric acid described above, it is desirable to prepare polymer-modified asphalt compositions without using polyphosphoric acid to accelerate the blending process.